Combined staring and scanning photodetector sensing system having both temporal and spatial filtering

Abstract

A photodetector sensing system is disclosed which combines staring and scanning features. By providing both temporal and spatial filtering, many system benefits are obtained. Each pixel in the viewed scene has a "dedicated" filter, which receives signals only from that pixel. By integrating time spaced signals from the same pixel, the filter maintains the staring effect of a two-dimensional detector array. A single detector may view a plurality of pixels, thereby improving resolution. A single pixel may be viewed by a plurality of detectors, thereby providing redundancy to correct for detector failures. The signal from each detector, after amplification, is first sent through a spatial, high frequency filter, and then is set to one of a plurality of parallel temporal, low frequency filters, which time share the detector. Synchronizing means are provided for ensuring that each temporal filter always receives its time spaced signals from the same source. Any suitable scanning mechanism may be used. The system may be used either to distinguish a moving target from a non-moving background, or to distinguish a non-moving target from a moving background.

What is claimed is: 
     
       1. A radiation sensing and decoding system comprising: an array of radiative/electronic transducer sensors each of which transmits signals independently of the other sensors;   a plurality of pixels observed by each sensor on a time-sharing basis;   a plurality of filters which receive as inputs the signals transmitted by each sensor; and   synchronizing means which control the operative time of each filter and which insure that it receives all of its input signals from the same pixel.   
     
     
       2. A radiation sensing and decoding system comprising: a plurality of photodetectors arranged in a two-dimensional focal plane, each detector having an individual electronic output;   scanning means, operating between the detectors and the observed radiation, for the purpose of causing each detector to view serially a plurality of separate radiation sources;   means for demultiplexing the electronic output signal of each detector to provide a plurality of parallel signals; and   means for synchronizing the scanning means to the demultiplexing means to insure that each parallel detector output signal receives input from the same radiation source at intervals determined by the scanning repetition frequency.   
     
     
       3. The system of claim 2 wherein: the demultiplexing means comprises a plurality of temporal bandpass filters connected in parallel to receive, on a time-sharing basis, the output signal from a single photodetector; and   the synchronizing means includes switching means which cause each of the temporal bandpass filters to be switched on while the others are switched off.   
     
     
       4. The system of claim 3 wherein each of the temporal bandpass filters includes: one or more high pass filters having a capacitor and a resistance-equivalent switched capacitance circuit; and   one or more low pass filters having a capacitor and a resistance equivalent switched capacitance circuit;   all switches in the switched capacitance circuits being switched off during the period when the respective bandpass filter is switched off by the synchronizing means, thereby isolating the charges of the capacitors in that filter until it is again switched on.   
     
     
       5. The system of claim 4 in which all switches which are either in the temporal bandpass filters or are used to switch those filters on and off are MOSFET transistors. 
     
     
       6. The system of claim 3 which also comprises: a high frequency spatial filter in the circuit between each photodetector and the plurality of temporal bandpass filters which time-share the photodetector.   
     
     
       7. The system of claim 6 which also comprises: preamplifier circuitry in series between each photodetector and its high frequency spatial filter.   
     
     
       8. The system of claim 4 wherein each temporal filter is matched to a particular pixel in the observed radiation field. 
     
     
       9. The system of claim 8 in which: the center-to-center distance between pixels is a fraction of the center-to-center distance between photodetectors; and   the scanning means causes each photodetector to view several spaced pixels, thereby increasing the resolution of the image received from the focal plane.   
     
     
       10. The system of claim 8 in which: the scanning means causes each pixel to be viewed by a plurality of detectors, thereby providing redundant output signals.   
     
     
       11. The system of claim 10 which also comprises: electronic logic circuitry for selecting a preferred output signal level from the redundant responses of a plurality of photodetectors to a single pixel.   
     
     
       12. The system of claim 11 in which: the center-to-center distance between pixels is a fraction of the center-to-center distance between photodetectors; and   the scanning means causes each photodetector to view several spaced pixels, thereby increasing the resolution of the image received from the focal plane.   
     
     
       13. The system of claim 12 in which: the frequency of pixel sampling is sufficient to cause overlapping of pixels, thereby oversampling to improve the image quality of the system.   
     
     
       14. The system of claim 8 in which: the scanning means causes a single pixel to be separately viewed by a photodetector in a plurality of spectral wave bands.   
     
     
       15. The system of claim 4 which also comprises: means for tuning the switching frequency of the switches in the switched capacitance circuits, thereby varying the electronic signal frequencies which pass through the temporal bandpass filters.   
     
     
       16. The system of claim 6 in which: the spatial filter includes one or more high pass filters having a capacitor and a resistance-equivalent switched capacitance circuit.   
     
     
       17. The system of claim 16 which also comprises: means for tuning the switching frequency of the switches in the switched capacitance circuit, thereby varying the electronic signal frequencies which pass through the spatial filter.   
     
     
       18. The system of claim 3 in which the temporal bandpass filters are located at the focal plane. 
     
     
       19. The system of claim 6 in which the spatial filter is located at the focal plane. 
     
     
       20. The system of claim 19 in which the temporal bandpass filters are located at the focal plane. 
     
     
       21. The system of claim 7 in which the preamplifier circuitry and the spatial filter are located at the focal plane. 
     
     
       22. The system of claim 21 in which the temporal filters are located at the focal plane. 
     
     
       23. The system of claim 15 in which the frequency to which the temporal bandpass filters are tuned is a function of the velocity of the intended target of observation. 
     
     
       24. The system of claim 17 in which the frequency to which the spatial filter is tuned is a function of the scan speed across each pixel. 
     
     
       25. The system of claim 6 in which: each of the temporal filters includes resistance-equivalent switched capacitance circuitry, the switching frequency of which is adjustable to tune the temporal filter pass-through frequency; and   the spatial filter includes resistance-equivalent switched capacitance circuitry, the switching frequency of which is adjustable to tune the spatial filter pass-through frequency.   
     
     
       26. The system of claim 25 in which the frequency to which the temporal filters are tuned is a function of the velocity of the intended target of observation, and the frequency to which the spatial filter is tuned is a function of the scan speed across each pixel, in order to provide target versus background discrimination regardless of their motion characteristics.